In recent years, different types of radio networks have been developed to provide wireless communication for various wireless devices in different areas. The radio networks are constantly improved to provide better capacity, quality and coverage to meet the demands from subscribers using services and increasingly advanced equipment, such as smartphones and tablets, which often require considerable amounts of bandwidth and resources for data transport in the networks. Therefore, it is often a challenge to achieve good performance, e.g. in terms of high data throughput, low latency and low rate of dropped or lost data, in the radio communication between network nodes in the radio network and various wireless devices communicating with the network nodes.
In order to improve the performance of such radio communication, various radio features can be employed that are intended to make the radio communication more efficient. For example, in radio networks operating according to Long Term Evolution, LTE, features such as Carrier Aggregation, CA, and Multiple Input Multiple Output, MIMO, are commonly used as defined by the third Generation Partnership Project, 3GPP. In carrier aggregation, multiple carriers are used simultaneously in radio communication with a wireless device, while in MIMO multiple data streams are conveyed using multiple antenna ports at the sender node and at the receiver node. Carrier aggregation and MIMO are employed mainly to increase data throughput for a wireless device.
In the field of radio communication, the term “wireless device” is commonly used and will be used in this disclosure to represent any terminal or device capable of radio communication including receiving downlink signals transmitted from a network node and sending uplink signals to the network node. Throughout this disclosure, wireless device could e.g. be exchanged for User Equipment, UE, which is another common term in this field.
Further, the term “network node”, also commonly referred to as a base station, radio node, e-nodeB, eNB, access point, etc., represents any node enabling radio access in a radio network which node can communicate uplink and downlink radio signals with wireless devices. The radio network may also be referred to as a cellular network for radio or wireless communication. The network nodes described in this disclosure may, without limitation, include so-called macro nodes and low power nodes such as micro, pico, femto, Wifi and relay nodes, to mention some customary examples. Throughout this disclosure, network node could e.g. be exchanged for base station or access point.
In carrier aggregation, a network node such as a base station or the equivalent is able to communicate radio signals with a wireless device simultaneously over two or more different carriers, sometimes referred to as Component Carriers, CC, corresponding to multiple cells serving the wireless device, which is illustrated by an example in FIG. 1. In this example, a network node 100 sends downlink signals to a wireless device 102 over three different carriers CC1, CC2 and CC3 which in turn provide coverage in three corresponding cells which may have overlapping or partly overlapping coverage. It should be noted that the configuration with three carriers and corresponding cells shown in FIG. 1 is just an illustrative example, and any number of carriers and cells may be employed for the carrier aggregation.
When serving the wireless device 102 with the carriers CC1, CC2 and CC3, one of the cells is appointed to act as a Primary cell, Pcell, in this example Pcell 1 which is served by a carrier CC1. The other two cells are appointed to act as Secondary cells, Scells, in this example Scell 2 and Scell 3 which are served by carriers CC2 and CC3, respectively. In this field of technology, a Pcell is defined as the “main” cell serving the wireless device such that both data and control signaling can be transmitted over the Pcell, while an Scell is defined as a supplementary cell that is typically used for transmitting data only, the Scell thus adding extra bandwidth to enable greater data throughput.
The above is applicable for both downlink and uplink signals. Further, the appointment of carriers, e.g. serving a Pcell and one or more Scells, is made per device such that a particular carrier may be used in a Pcell for one wireless device and in an Scell for another wireless device. For example in FIG. 1, the carrier CC1 which is used for serving the device 102 in a Pcell could at the same time be used for serving another device in an Scell, not shown. Similarly, the carrier CC2, or CC3, which is used for serving the device 102 in an Scell could at the same time be used for serving another device in a Pcell, not shown.
Carrier aggregation may thus be used in radio communication with a wireless device to support wider transmission bandwidths and thus higher data throughput. The wireless device must have reception and/or transmission capabilities for carrier aggregation such that it can simultaneously receive and/or transmit on multiple carriers, which is the case for wireless devices configured according to the third Generation Partnership Project, 3GPP, Rel-10 or later. In this way, the network node is able to serve several cells with basically the same coverage area as shown in FIG. 1, or with different coverage areas, at different carrier frequencies.
Carrier aggregation can be used both for uplink communication and for downlink communication. Further, it is possible to configure a wireless device to aggregate a different number of carriers in the uplink than in the downlink, still originating from the same network node, thus enabling different bandwidths in uplink and downlink. The maximum number of downlink carriers that can be configured for a wireless device depends on the downlink aggregation capability of the device. Similarly, the maximum number of uplink carriers that can be configured depends on the uplink aggregation capability of the device.
In MIMO, multiple antenna ports are used both at a sending node and at a receiving node in order to convey multiple spatially separated data streams between the sending and receiving nodes. MIMO can likewise be used both for uplink communication and for downlink communication. In uplink communication, the wireless device is the sending node and the network node is the receiving node, while in downlink communication, the network node is the sending node and the wireless device is the receiving node. According to LTE Rel-8, a network node can have 1, 2, or 4 physical antenna ports, and different reference signals are sent out on these antenna ports. In later releases, it is also possible to configure more than four antenna ports.
A wireless device can indicate, by signaling to its serving network node, its capability to support various features that can be configured by the network, such as multiple data streams in downlink and/or uplink communication within a reported frequency band. This signaling is commonly referred to as “UE capability signaling” which term is used throughout this disclosure to indicate signaling from a wireless device of its capability to use one or more radio features. Moreover, the network node can schedule data on one or more data streams in downlink and/or uplink via physical control channels and/or MAC control elements which are signaled to the wireless device.
As mentioned above, a specific radio feature, such as carrier aggregation using a specific number of carriers, or MIMO using a specific number of data streams or MIMO layers, may be employed in a network node which feature is intended to improve performance in the radio network, e.g. in terms of throughput. In order for the network node to be aware of which radio network features that are supported by a particular wireless device and can be used in a radio communication with the wireless device, the network node is able to request device capability information from the device to indicate what features the device supports. The device then responds with indicators of its supported radio features, either one indicator per feature or via feature group indicators where several radio features are indicated together. Such an indicator thus indicates whether the one or more radio features are supported or not.
The current UE capability signaling in case of intra-band contiguous carrier aggregation only allows the wireless device to signal UE capabilities that are applicable to all component carriers in a particular band. The lack of capability indication for each individual carrier requires that the UE always signals the minimum, or least, capability supported for all CCs, even though a greater or higher capability may be supported for a subset of the carriers, e.g. for one carrier. As a result, the device's true capability is possibly underutilized in case of contiguous carrier aggregation since the signaled minimum capability must be respected, i.e. not exceeded, when configuring radio features for the wireless device. It is thus a problem that the wireless device is sometimes restricted to use less radio features, e.g. less MIMO layers, than it is actually capable of using. With the introduction of higher order carrier aggregation (3CCs or more), this limitation may become even more notable for advanced devices and advanced features to be deployed in the radio network.